Pump-free and high-throughput generation of monodisperse hydrogel beads by microfluidic step emulsification for dLAMP-on-a-chip

Abstract

Step emulsification (SE), which generates droplets by a sharp change in confinement, has emerged as a potential alternative to flow-focusing technology. Water/dispersed phase is continuously pumped through a shallow inlet channel into a deep chamber pre-filled with the oil/continuous phase. The need for one or more pumps to maintain a continuous flow for droplet generation, and the consequent use of high sample volumes, limit this technique to research labs. Here, we report a pumpfree SE technique for rapid and high-throughput generation of monodisperse hydrogel (agarose) beads using <40 {micro}l sample volume. Instead of using syringe pumps, we sequentially pipetted oil and liquid agarose into a microfluidic SE device to generate between 20000 and 80000 agarose beads in [~] 2 min. We also demonstrated the encapsulation of loop-mediated isothermal amplification mixture inside these beads at the time of their formation. Finally, using these beads as reaction chambers, we amplified nucleic acids from P. falciparum and SARS-CoV-2 inside them. The pump-free operation, tiny sample volume, and high-throughput generation of droplets by SE make our technique suitable for point-of-care diagnostics.